Tubular members have long been known as structural elements in various applications. The manner in which such elements are joined has been the subject of the following patents of which I am aware:
The Cronin patent, U.S. Pat. No. 3,071,399, discloses a joint for tubular members wherein one or more tubular members are received in apertures of another tubular member with one of the received tubular members being an expandable sleeve internally mounted such that rotation of screw expands a portion of the received tubular member inside the receiving tubular member, thereby preventing withdrawal of the received members. This appears to be a permanent lock.
The Frieberg patent, U.S. Pat. No. 4,169,573, discloses a joint assembly in which a first tubular member receives a pair of orthogonal tubular members in apertures therein with a fastener connecting the orthogonal members internally of the first tubular member to prevent their withdrawal.
The Chapman et al patent, U.S. Pat. No. 4,294,561, discloses a joining member for receiving orthogonal tubular members therein and a means for securing the members by engaging only one of the members received within the joining member.
Nasi, U.S. Pat. No. 4,406,562, discloses an assembly node which is formed from a plurality of interlocking flat elements which are connected together as by welding.
Each of the above devices, except Nasi, requires the use of a fastener or is directed to a fastener. Nasi is directed to a node which is in essence a fastener for connecting elements in a spatial structure. None of the devices relies on the particular combination of apertures to achieve the interlocking connection as does the present invention nor does a combination of these devices suggest interlocking of tubular members.